Tyvek makes a very good boot, but it does degrade over time, so you need to replace it periodically. I had to replace my tires last October due to a double blowout (hit an invisible pothole at speed and it trashed both tires beyond repair), and got a fairly deep cut in the new rear tire fairly quickly. Booted it and forgot about it. I tested some different tires 3 weeks ago, and the tyvek was degraded to the point where I could tear it by hand. I suppose the heat and friction of constantly bending eventually degrades the material.